Cancer-causing chemicals linger around homes and in gardens over a 9-square-mile area more than three months after a catastrophic fire at the Chevron refinery in Richmond, according to an environmental justice group.

Independent testing by Global Community Monitor found that toxic fallout from the giant plume of smoke and soot that spewed from the plant on Aug. 6 blanketed an area stretching from Albany to San Pablo with dangerous hydrocarbons.

Five of eight samples of dust at different residential locations around the refinery had high levels of polycyclic aromatic hydrocarbons, or PAHs, in the dust and soil, said Denny Larson, executive director of the Richmond group, which tests for toxic substances in urban communities and advocates for tighter regulations and monitoring.

Among the carcinogenic compounds was benzo(a)pyrene, according to the laboratory analysis done by ALS Environmental in Kelso, Wash.

'Potent carcinogens'

"PAHs are extremely hazardous. They are one of the most potent carcinogens in existence," said Larson, adding that people, particularly outdoor gardeners, can inhale the dust, accumulate it through skin contact and eat it in produce. "We felt it was important to let people know that this stuff is still out there so that people can take the proper precautions."

Sean Comey, a spokesman for Chevron, questioned the results. "The conclusion of independent experts is that there is not a significant risk from the August 6 fire," he wrote in an e-mail. That's based on "air samples the Contra Costa County health department and the Bay Area Air Quality Management District took during the fire."

Wendel Brunner, director of the county's health department, could not be reached for comment.

The fire is believed to have been caused by hydrocarbon vapor leaking from a corroded pipe. It sent noxious smoke wafting over the East Bay, forcing thousands to seek shelter indoors and prompting 15,000 people to seek treatment at local hospitals.

Federal authorities are conducting a criminal investigation into accusations that Chevron, unbeknownst to regulators, piped pollutants around monitoring equipment at the refinery for four years and burned an unknown quantity of gases off into the atmosphere. California workplace regulators are also probing safety practices.

Still, nobody has been able to quantify exactly how many toxic chemicals were released into the community. Chevron officials have insisted that the white plume seen rising over the refinery just before the fire was mostly steam.

The Bay Area Air Quality Management District, which is responsible for protecting air quality in the nine Bay Area counties, concluded after initial testing that all but one of the toxic pollutants commonly associated with petroleum production were at background levels during the fire and did not pose a significant health risk.

The problem, according to environmental analysts, was that only two of the eight air-quality monitoring stations in the area are in Richmond - and none is at the refinery.

Risk unknown

Larson said inadequate monitoring prompted his group to do its own testing. It is unclear what danger short-term exposure to the chemicals can pose, but Larson said the regulatory agencies should at least be conducting tests and warning people.

"Everybody agrees they are very potent carcinogens and that they have all these really nasty properties, but when it comes to judging the danger of a single event like this, there are no benchmarks or reference levels to judge the effect," Larson said. "Can we say that the exposure level was enough to bump anyone over to manifesting cancer? No. But it could be possible that this in combination with exposures over a lifetime could have a significant impact on a person's health."